1. Field of the Invention.
The present invention relates generally to laminated parts. More particularly, the present invention relates to lamina stacks, and especially long, slender lamina stacks, formed by stamping a plurality of lamina layers from a sheet or strip of stock material and the methods and apparatuses, i.e., progressive dies, used in the manufacture of such laminated parts, and ignition coils which incorporate the laminated parts.
2. Description of the Related Art.
The manufacture of parts, e.g., stators and rotors for electric motors, employing stacked laminae is well known in the art. Typically, the laminae are blanked from a continuous strip stock and then stacked and bound together to form the completed part. Progressive die assemblies for producing laminated stacks, wherein a strip of lamina material is fed through a sequence of punching steps to progressively form the laminae to the desired end configuration, are also well known.
It is also known to form, in the laminae, interlock tabs which extend below the generally planar lamina surface and engage slots formed in the next lower lamina. In this manner, a plurality of laminae may be stamped from a single sheet of strip stock and formed into an interconnected lamina stack in the die by means of interlocking tabs and slots. More specifically, to form an interconnected lamina stack each lamina, except the bottom lamina of the stack, may have a plurality of arcuately spaced interlock tabs (typically ranging from 3 to 8 circumferentially disposed tabs) depressed from the lamina lower surface adjacent to slots formed in the next lower lamina. Each interlock tab engages a corresponding slot in the next lower lamina of the stack, generally by the entire thickness of the tab. The bottom lamina of the stack may have the interlock tabs blanked and removed to avoid interlocking the bottom lamina with the next lower lamina which forms the top lamina of the previous stack. In rare instances the tab may lock as deeply as two lamina thicknesses, in which case two end laminae must be blanked.
Rotor laminae generally include a plurality of skewed conductor slots which are formed around the periphery of the rotor stack in arcuately spaced relation to one another. The conductor slots are arcuately spaced in an individual lamina in a fixed relationship to one another and, in a rotor stack, are skewed relative to an adjacent lamina by rotationally indexing the partially completed rotor stack with respect to the last produced lamina being attached thereto. Indexing involves rotating the rotor stack and the last produced lamina relative to each other by a predetermined rotational increment so that, when the laminae are combined in a stack, the rotor conductor bar slot defined by adjacent conductor slots are skewed or slanted relative to the stack axis. Stator stacks, on the other hand, include winding slots around the inner periphery of the stack which extend parallel to the stack axis, without skew, and are shaped to receive the stator windings. In some circumstances, however, it may be desired to build an xe2x80x9cinside-outxe2x80x9d motor wherein the outer lamina stack forms the rotor and would, thus, require skewed slots.
Another system of forming a stack involves loosely stacking the laminae as they are formed and blanked from the stock material in a progressive die assembly. After all the laminae for a given stack are collected, they are shuttled to a pressing station and the laminae are pressed together to engage the interlock tabs and thereby form the lamina stack. Loosely stacking the laminae after they are blanked from strip stock has several disadvantages; loose stacking and subsequent pressing does not as consistently lock adjacent laminae together; the required handling slows production times; and the system lacks a means for automatically correcting thickness inconsistencies of the stock material or creating a desired skew angle for the conductor slots. A similar process can be employed without the use of interlocking features on the laminae. Assembly of the non-interlocked laminae requires the welding, keying or riveting (or pinning) of the laminae to interconnect the laminae in a stack.
In response to these problems, an autorotation system for compensating for the nonuniform stock thickness was developed which both rotates and interlocks the stacked laminae. This system compensates for variations in lamina thickness while still properly skewing the conductor slots of rotor laminae, as described in U.S. Pat. Nos. 4,619,028; 4,738,020; 5,087,849 and 5,123,155, all assigned to the assignee of the present invention and the disclosures of which are incorporated herein by reference. In the system disclosed in the aforementioned patents, the choke barrel or passageway holding the lamina stack may be automatically rotated before each lamina is blanked from the strip stock and the lamina""s circumferentially disposed tabs are interlocked with the slots of the uppermost lamina of the incomplete lamina stack within the barrel. Alternatively, the choke may be automatically rotated with every other press cycle, every third press cycle, and so on.
In the apparatus and method disclosed in the aforementioned patents, the individual laminae are typically rotated through an angle of 180xc2x0. Although the laminae may be rotated through other angles, the angle must be at least 360xc2x0/(number of interlock tabs) so that the interlocking tabs and slots are properly aligned.
The above described improvements have been implemented with rotor laminae and stator laminae which have identical outer perimeters which enables their insertion into a choke barrel designed to hold a lamina having the outer perimeter configuration of the laminae being stacked. Many of these improvements require the use of interlock tabs in combination with autorotation of a partially formed lamina stack.
Autorotation requires the use of a rotating choke barrel which firmly holds the partially formed lamina stack in position as blanked laminae are forced into engagement with the uppermost lamina of the stack. The choke barrel is typically configured to match the outer perimeter of the blanked lamina and may be slightly undersized, e.g., by 0.001 inch, so that the laminae will be firmly held and accurately positioned within the choke barrel. The laminae, after they are located in the choke barrel with an interference fit thereby provide back pressure or resistance which facilitates the entry of the interlock tabs of the next lamina when it is pressed into the choke barrel.
In certain applications, however, it is desirable to have a lamina stack, typically a stator core but also rotor cores in some situations, wherein some of the laminae have an outside perimeter which differs in shape and/or size from the remainder of the stack of laminae, i.e., the laminae in the stack have a plurality of distinguishable configurations. For example, the stator core may incorporate a fastening feature, such as a projecting flange, to provide a mounting surface which is integral with the stator core, or the stator may incorporate a sealing feature to provide a seal between the housing of the motor and the stator core for motors to be used in environments which include flammable vapors. To incorporate such features, a fraction of the laminae in a stack are manufactured with integral portions which provide such features.
Traditionally, the manner in which stator cores having a plurality of outer perimeter configurations have been produced is to stamp the differently configured laminae in separate dies, i.e., each die provides only a single lamina configuration. The plurality of dies produce loose laminae having the desired plurality of outer perimeter configurations. The laminae must then be manually assembled at a station where laminae of the different outer perimeter configurations are placed in the proper vertical stack arrangement and are pressed together to interlock the laminae. Instead of using interlocking tabs, the laminae may also be secured together in some other conventional fashion such as by the use of clamps, pins, rivets or welds.
There are several drawbacks to this manner of manufacturing a lamina core having laminae with a plurality of outer perimeter configurations. For one, the manufacturing process is relatively expensive due to the use of multiple dies and the large amount of labor and handling which is required. Further, production rates with this process tend to be relatively slow. Additionally, the process does not allow for the automatic correction of lamina thickness inconsistencies.
Another problem with this method of manufacture is that it often produces stator cores having winding slots with slight discontinuities and sharp edges. Because separate dies are used to form the differently configured laminae, the stator winding slots are punched by different dies. Although similar in shape, the different punches cannot be precisely identical and will generally have minor inconsistencies which, when the differing laminae are stacked, cause the slots in adjacent laminae to misalign, thereby creating slight discontinuities and sharp edges in the winding slots at the points where the two differently configured laminae meet. These small discontinuities can scratch and damage the winding coil wires which are inserted into the winding slots.
The discontinuities of the projections which define the winding slots and interior surface of the stator core also reduce the efficiency of the electric motor or generator which is produced with the stator core. The efficiency of the motor or generator may be reduced if the gap between the stator core and rotor core is enlarged to account for the discontinuities present on the interior surfaces of the stator core because the efficiency of the motor or generator is decreased as the gap increases.
The manufacture of lamina stacks wherein individual laminae are comprised of two or more discrete segments also presents significant manufacturing difficulties. It is often impractical to manufacture lamina stacks wherein one or more of the laminae is formed by at least two discrete lamina segments. Laminae comprised of a plurality of discrete segments present difficulties in maintaining the proper alignment between the various lamina segments which comprise the individual lamina and between the lamina segments and the other laminae which comprise the remainder of the lamina stack.
Further, in certain applications it is desirable to have a stack of interlocked laminae which is long and slender, and which has a cross-sectional shape having lateral sides defined by the lamina outer edges which do not lie in a substantially common plane; such a stack does not provide a choke-engaging surface which extends substantially along the vertical height of the stack. For example, it is desirable to have an elongate, substantially cylindrically-shaped lamina stack, in which the first, bottommost lamina is narrower than the adjacent, overlying second lamina, which is narrower than the adjacent, overlying third lamina, and so on, with the middlemost lamina(e) defining the widest portion of the substantially circular cross section and subsequent adjacent, overlying laminae each having a reduced width as compared to its adjacent lamina, thus forming a circular cross section, with each of the laminae of the cylindrically-shaped stack interconnected. Notably, the stock material from which a lamina stack may be produced according to the present invention is thin, and the individual laminae stamped therefrom quite flexible. Because the individual laminae of such a stack are long, thin and flexible, and may also have common choke-engaging edges forming a planar choke engaging surface only at the longitudinal ends of the stack, the individual laminae tend to inadequately support the stack in the choke opening or to cause the laminae to bow, rendering the above-described automatic interlocking method unusable for manufacturing such stacks. Moreover, the above-described automatic interlocking method may also be difficult to use in producing interlocked stacks of laminae which are long, thin and flexible, but do have common choke-engaging edges forming a planar surface at the lateral sides of the stack. Prior art manufacturing methods for attaching the long, thin flexible laminae of these stacks together include post-stacking welding, keying or riveting operations or a separate pressing operation for engaging the interlocking tabs, as such prior art operations do not require the laminae to be firmly held and accurately positioned within a choke opening.
Among other applications, the stacked, interlocked lamina structures of the present invention have been determined to be useful in coil-on-plug type ignition coil assemblies. Such assemblies which are exemplified by U.S. Pat. No. 5,870,012 and Kikuta et al., include both a wound primary coil and a wound secondary coil. At the proper time in the engine operating cycle, electric current flowing through the primary coil of the respective ignition coil assembly is abruptly interrupted to induce a voltage in the secondary coil that is sufficiently high enough to create a spark across gapped electrodes of the spark plug that are disposed within a combustion chamber space of the respective engine cylinder, causing ignition of a combustible fuel-air
What is needed is an apparatus and method for producing long, slender, interlocked stacks of flexible laminae in which the laminae are automatically stamped, stacked and interlocked, the stacks having cross-sectional shapes with side surfaces defined by the side edges of the laminae which may or may not commonly engage the adjacent choke surfaces.
The present invention provides an apparatus and method for manufacturing and automatically stacking a laminated stack which includes a lamina comprised of a plurality of discrete lamina segments and which may include a plurality of differently configured laminae to thereby produce lamina stacks which may include a plurality of slots and windows separating individual lamina segments. The present invention also provides an apparatus and method for producing long, slender, interlocked lamina stacks wherein the individual laminae have cross-sectional shapes having sides which do not substantially lie in a common plane.
An advantage of the present invention is that it permits the automatic stacking of a laminated stack which includes a lamina layer comprised of discrete lamina segments thereby providing for the economical manufacture of lamina stacks which include a lamina or lamina layer comprising a plurality of discrete lamina segments. For example, linear motors which require stator cores having slots on opposing sides of the core for accommodating supports for an actuator disposed within the stator core may be economically manufactured by the present invention. The ability to automatically stack a lamina comprised of discrete lamina segments also permits the manufacture of a wide variety of laminated stacks for applications beyond electrical motor and stator cores which are uneconomical or impractical to manufacture using laminated stacks which do not include laminae comprising discrete lamina segments.
Another advantage of the present invention is that the economical manufacture of laminated stacks comprising a lamina layer of discrete lamina segments permits the manufacture of parts which were previously stamped from a single thickness stock material. Manufacturing parts from laminae rather than from a single thickness stock material can eliminate secondary operations. For example, notches can be placed in selected laminae prior to stacking to thereby form a notch or opening in the outside edge or wall of the laminated stack which does not extend the entire height of the stack and which, if formed in a part stamped from a single thickness of stock material, would require a secondary machining operation after stamping.
Yet another advantage of the present invention is that it permits the automatic stacking of a laminated stack having a plurality of distinguishable outer perimeter configurations. The need to manually handle and stack laminae to form a lamina stack having a plurality of outer perimeter configurations and/or a lamina layer comprising a plurality of discrete segments is thereby eliminated. The conveyor, pressing and stack securing equipment used in the traditional manual assembly method are also eliminated by the present invention.
Yet another advantage of the present invention is that it permits the automatic stacking of long, thin, flexible laminae into an interlocked stack, the laminae having cross-sectional shapes with sides that may not substantially lie in a common plane.
The invention comprises, in one form thereof, a die assembly for producing a lamina stack including at least one lamina layer which is comprised of a plurality of discrete segments. Strip stock is guided through the die assembly and a plurality of laminae and discrete lamina segments are progressively stamped from the strip stock. The laminae and each of the discrete lamina segments have interlock tabs and/or slots punched therein and remain attached to the strip stock prior to advancement to the blanking station at which the choke barrel is located. At the blanking station, the lamina segments have their interlock tabs engaged with the interlock slots of the uppermost lamina in the choke barrel immediately prior to the complete separation of the lamina segments from the strip stock material thereby maintaining the lamina segments in proper alignment with each other and the laminae which form the remainder of the lamina stack. The choke barrel may also be rotatable whereby the laminae may be rotated to correct for thickness inconsistencies in the strip stock material.
The invention comprises, in another form thereof, a die assembly for producing a lamina stack including at least one lamina which is comprised of a plurality of lamina segments and wherein the laminae forming the stack have more than one predetermined outer perimeter configuration. The die assembly provides for the alignment, interlocking and stacking of the lamina segments as described above and also provides a common choke surface on the outer perimeter of each of the lamina segments so that, when the lamina stack is completed, the resultant stack comprising lamina layers having a plurality of outer perimeters and may have a plurality of common choke surfaces on its outer perimeter which may extend continuously along the exterior edge of each lamina layer in the stack in a direction parallel to the axis of the lamina stack. The laminae are stacked within the choke barrel such that the common choke surfaces are in registry with an alignment surface of the choke barrel.
The invention comprises, in another form thereof, a selectively actuated die assembly for producing a lamina stack formed from laminae which have more than one predetermined outer perimeter configuration. Each of the differing outer perimeter configurations has at least one common choke surface so that, when the laminae are stacked, the resultant stack may have at least one choke surface on its outer perimeter which extends continuously along the exterior edge of each lamina in the stack in a direction parallel to the axis of the lamina stack. The laminae are then stacked in a choke barrel with their common choke surfaces being aligned to create a lamina stack comprised of laminae having a plurality of outer perimeters and at least one choke surface extending continuously in an axial direction across a portion of the outer perimeter of each of the laminae. The choke barrel, which may be rotatable, includes an alignment surface, the common choke surfaces of the laminae being stacked in registry with the alignment surface.
The invention comprises, in another form thereof, a method of manufacturing a lamina stack, having at least one lamina layer formed from a plurality of discrete segments, in a die assembly having a punch and a choke barrel. Strip stock is guided through the die assembly and a plurality of laminae are stamped from the strip stock including at least one lamina which is comprised of at least two discrete segments. The lamina segments are maintained in relative alignment by attachment to the strip stock material as they are advanced through the die assembly. During progression of the discrete segments through the die assembly interlock tabs and slots are stamped into each of the lamina segments. When the lamina segments reach the choke barrel, the interlock tabs of each of the lamina segments are engaged with the uppermost lamina in the choke barrel prior to separating the discrete segments from the strip stock to thereby continuously maintain the proper alignment of the lamina segments relative to each other and the other laminae which form the remainder of the lamina stack.
The invention comprises, in another form thereof, a method of manufacturing a lamina stack in a die assembly having a selectively actuated punch and a choke barrel. Strip stock is guided through the die assembly and a plurality of laminae are stamped from the strip stock by the selectively actuated punch to form laminae having a plurality of outer perimeter configurations. The laminae each have a common choke surface which are aligned as the laminae are formed into a stack in the choke barrel. It is also possible to autorotate the laminae prior to stacking the laminae.
The invention comprises, in another form thereof, a method of manufacturing an elongate laminated stack in a die assembly having means for guiding strip stock material through the die assembly, stamping means and a choke passageway or opening. A first elongate lamina is stamped in the stock material and at least one first interlock means for engaging another lamina is stamped in the first lamina. The first lamina is separated from the stock material and placed into the choke passageway. A second lamina is stamped in the stock material and at least one second interlock means for engaging another lamina is stamped in the second lamina. The first and second interlocking means are at least partially engaged, after which the second lamina is separated from the stock material and placed into the choke passageway. While in the choke passageway, only one of the first and second laminae frictionally engages the choke passageway along its first and second elongate edges.
The invention comprises, in another form thereof, a method of manufacturing an elongate stack of laminae in a die assembly having means for guiding strip stock material through the die assembly, stamping means and a choke passageway. A first lamina is stamped in the stock material and at least one first interlock means for engaging another lamina is stamped in the first lamina. The first lamina is separated from the sheet stock material to yield a first lamina having a first outside perimeter shape having an elongate edge and which is placed into the choke passageway. A second lamina is stamped in the stock material and at least one second interlock means for engaging another lamina is stamped in the second lamina. The first and second interlocking means are at least partially engaged before the second lamina is separated from the stock material. The second lamina is separated from the sheet stock material to yield a second laminar segment having a second outside perimeter shape having an elongate edge and different than the first outside perimeter shape, and is placed into the choke passageway. The elongate edge of only one of the first and second laminae frictionally engages the choke passageway.
The invention comprises, in another form thereof, a method of manufacturing an elongate stack of interlocked laminae in a die assembly having means for guiding strip stock material therethrough, stamping means and a choke passageway or opening. The method includes stamping a first elongated lamina having generally opposed first, second, third, and fourth edges in the strip stock material. At least one first interlock element is also stamped into the first lamina, after which the first lamina is separated from the strip stock material and placed into the choke passageway, the first and second edges of the first lamina frictionally engaging the choke passageway. A second elongate lamina having first, second, third, and fourth edges is stamped in the strip stock material. At least one second interlock element is also stamped in the second lamina and at least partially engaged with the first interlocking element, after which the second lamina is separated from the strip stock material and placed into the choke passageway, the first and second edges of the second lamina frictionally engaging the choke passageway. The choke passageway frictionally engages along the third and fourth edges of only one of the first and second laminae.
The invention comprises, in another form thereof, a die assembly for manufacturing a stack of elongate, slender laminae from strip stock material, which comprises a plurality of punching stations, each punching station having a punch for stamping features in strip stock material. The features define elongate laminae each having generally opposite first and second edges and interlock means for engaging another lamina. Each of the laminae are connected to a carrier portion of the strip stock material. The die assembly further includes aligning means for positioning the strip stock material in the die assembly, and a blanking station having a blanking punch disposed over an elongate choke cavity for separating a lamina from the carrier portion of the strip stock.
The invention comprises, in yet another form thereof, an elongate stack of laminae including at least one first lamina and at least one second lamina, the first lamina being the widest of all laminae in the stack. The second lamina has a width which is less than that of the first lamina. Each lamina in the stack is interlocked to another lamina.
The invention comprises, in still another form thereof, an elongate stack of interlocked laminae including a first elongate, slender, relatively flexible lamina having a first interlock element and first and second generally opposed edges defining the ends of the first lamina in a first direction of the stack. The first lamina also has third and fourth generally opposed edges defining the ends of the first lamina in a second stack direction. The stack also includes a second elongate, slender, relatively flexible lamina having a second interlock element, which is interlocked with the first interlock element, and first and second generally opposed edges defining the ends of the second lamina in the first stack direction. The first edges of the first and second laminae are aligned to define a substantially planar stack surface. The second lamina also has third and fourth generally opposed edges defining the ends thereof in the second stack direction. One of the third and fourth edges of the first lamina are not aligned with the third and fourth edges of the second lamina.
The invention comprises, in yet another form, an ignition coil assembly for an internal combustion engine that incorporates a cylindrical core element formed from a stack of interlocked laminae.